Differential detection in cable television

Analog fiber links often use externally modulated 1550 nm transmitters and EDFAs to obtain high performance over long distances. The use of differential detection eliminates two signal-degrading effects associated with such transmission phase to amplitude noise conversion, and fiber-induced composite second order distortion (CSO). In addition, the use of differential detection boosts the net carrier-to-noise ratio (CNR) by 3 dB, and enables very high analog performance over distances in excess of 50 km, without the use of optical amplifiers.